High temperature thermal processing techniques are commonly used to convert hydrocarbon feedstock material to more valuable products. Depending on the feedstock material and desired products, some processes require high temperatures to trigger the desired reactions. For example, high temperatures are used to crack various hydrocarbons into lighter products.
In other processes, high temperatures are required both to trigger the desired reactions as well as to provide the enthalpy necessary for formation of the desired products. For example, various thermal processing techniques are used to convert methane directly to C2 hydrocarbons, such as acetylene via reaction (1), ethylene via reaction (2), and ethane via reaction (3).2CH4→C2H2+3H2  (1)2CH4→C2H4+2H2  (2)2CH4→C2H6+H2  (3)
These reactions are highly endothermic, requiring approximately 377 kJ/mol, 202 kJ/mol, and 65 kJ/mol, respectively. In addition, higher temperatures are required to achieve high conversion of the feedstock and high selectivity to the desired product.
One type of thermal processing used in the prior art involves exposing the feedstock to high temperature combustion gases causing the feedstock to pyrolyze into the desired unsaturated product. Many traditional processes involve steam cracking, while other processes involve combustion.
The formation of acetylene from methane by thermal processing is difficult because of the relative free energies of formation of methane and acetylene. Above 800 K, CxHy compounds may undergo decomposition into carbon and hydrogen. Below 1500 K, the free energy of formation of methane is above that of acetylene. As such, the formation of methane, the final product of thermodynamic equilibrium, is favored over acetylene between the temperatures of 800 K and 1500 K. Above 1500 K, however, the free energy of formation of acetylene is lower than that of methane. As a result, the formation of acetylene is favored over that of methane. But, as the reactants are cooled below 1500 K, the thermodynamic equilibrium shifts back to methane and the acetylene produced at the higher temperature will decompose and reform as methane. Acetylene and the other hydrocarbons can continue to react to form aromatic and polyaromatic species. When water and carbon dioxide are present acetylene can react to form carbon monoxide which is less valuable product than acetylene. Methane is a very refractory material and as such the pyrolitic reaction of methane to form acetylene and other desired hydrocarbons has a high activation energy. The decomposition reactions of acetylene have lower activation energy and thus the formation of acetylene is favored by reacting at high temperatures but with short controlled residence times that minimize consecutive reactions of acetylene with additional acetylene, hydrocarbons and oxygen containing species such as H2O, CO2 and O2. As such, the conversion of methane to acetylene in this manner necessarily requires processing at high temperatures.
Prior art reactors, however, can operate for only short periods of time before components of the reactor are adversely affected by the high temperatures. As such, these reactors can fail prematurely or require excessive maintenance or shutdowns. For large-scale production, however, it is desirable to operate reactors continuously for long periods of time on the order of months, or longer.
Accordingly, it would be an advance in the state of the art to provide a pyrolitic reactor having a cooling means that enables sustained, high-temperature, steady state operation, for a prolonged period of time.